Gene therapy is used to treat hereditary diseases such as cystic fibrosis and also acquired diseases such as cancers [M. Conese, et al., Journal of Cystic Fibrosis (2011) 10, S114], but is only as effective as its ability to deliver the therapeutic polynucleotide to a desired location. Vectors for gene delivery may be viral or nonviral. Viral vectors offer highly efficient gene transfer, but unwanted immune stimulation and the potential for mutagenesis have virtually eliminated them from clinical trials [M. L. Edelstein, et al., Journal of Gene Medicine (2007) 9, 833; C. E. Thomas, et al., Nature Reviews Genetics (2003) 4, 346]. In contrast, nonviral vectors are safe, have low immunogenicity, and are relatively inexpensive [J. F. Guo, et al., Biotechnology Advances (2011) 29, 402].
Examples of nonviral vectors include bacteria [C. H. Chang, et al., Biotechnology and Bioengineering 2011, 108], cell penetrating peptides [Y. A. Chen, et al., Biomaterials 2011, 32, 4174], functionalized gold nanoparticles or carbon nanotubes [C. M. McIntosh, et al., Journal of the American Chemical Society 2001, 123, 7626; G. Han, et al., Chemical Biology & Drug Design 2006, 67, 78; G. Han, et al., Bioconjugate Chemistry 2005, 16, 1356; L. Z. Gao, et al., Chembiochem 2006, 7, 239], and cationic polymers. Among these nonviral vectors, cationic polymers including polyethyleneimine (PEI) [U. Lungwitz, et al., Eur. J. of Pharmaceutics and Biopharmaceutics 2005, 60, 247], poly(1-lysine) (PLL) [U. Lungwitz, et al., Eur. J. of Pharmaceutics and Biopharmaceutics 2005, 60, 247; T. L. Kaneshiro, et al., Molecular Pharmaceutics 2007, 4, 759], chitosan [K. Corsi, et al., Biomaterials 2003, 24, 1255], dendrimers 9J. Dennig, Dendrimers V: Functional and Hyperbranched Building Blocks, Photophysical Properties, Applications in Materials and Life Sciences 2003, 228, 227; H. M. Wu, et al., Biomaterials 2011, 32, 1619] and cationic lipids [M. Morille, et al., Biomaterials 2008, 29, 3477] have the advantages of being scalable for manufacturing in quantity, having low immunogenicity, the capacity for selective chemical modification and the ability to carry large inserts. Due to its superior transfection efficiency in a broad range of cell types, synthetic PEI has a privileged place among nonviral gene delivery systems. However, the high number of positive charges on PEI and its lack of biodegradability make it toxic in vivo and has thus hampered clinical applications [U. Lungwitz, et al., Eur. J. of Pharmaceutics and Biopharmaceutics 2005, 60, 247; T. L. Kaneshiro, et al., Molecular Pharmaceutics 2007, 4, 759].
Chitosan, which is obtained by deacetylation of chitin, is a biocompatible and biodegradable linear polymer whose cationic polyelectrolyte nature provides strong electrostatic interaction with negative charged DNA to form stable complexes that protect the DNA from degradation. However, the transfection efficiency of chitosan is very low and is dependent on its molecular weight, size and percentage of deacetylation [H. L. Jiang, et al., Journal of Controlled Release 2007, 117, 273]. The goal of a successful nonviral gene delivery system, therefore, is to achieve therapeutic efficacy while minimizing toxicity [M. Breunig, et al., Proceedings of the National Academy of Sciences of the United States of America 2007, 104, 14454]. To develop such a safe and effective delivery vehicle, PEI-grafted chitosan, chitosan-grafted PEI or a chitosan-PEI composite have been tested and shown to have improved transfection efficiency and reduced toxicity compared to PEI alone [Y. L. Lou, et al., Journal of Biomedical Materials Research Part A 2009, 88A, 1058; D. Jere, et al., International Journal of Pharmaceutics 2009, 378, 194; H. L. Jiang, et al., Gene Therapy 2007, 14, 1389; H. L. Jiang, et al., Journal of Biomedical Nanotechnology 2007, 3, 377].
For advanced gene therapy, it is desirable to be able to monitor the in-vivo gene delivery in real time. Magnetic resonance imaging (MRI) is a powerful clinical imaging technique for diagnosis of a variety of diseases and post-therapy assessment. MRI contrast can be enhanced by the use of positive or negative contrast agents resulting in brighter (T1-weighted) or darker (T2-weighted) images, respectively. Superparamagnetic iron oxide nanoparticles (SPIONs) are T2 contrast agents that are widely used in molecular and cellular imaging applications [P. Zou, et al. Sun, Molecular Pharmaceutics 2010, 7, 1974; R. Chen, et al., International Journal of Nanomedicine 2011, 6, 511]. Recently, PEI-poly(ethylene glycol) (PEG)-chitosan coated SPIONs have been reported for DNA or siRNA delivery and MRI imaging [F. M. Kievit, et al., Advanced Functional Materials 2009, 19, 2244; O. Veiseh, et al., Biomaterials 2010, 31] and PEG-grafted PEI-complexed SPION for gene delivery and MRI imaging [G. Chen, et al., Biomaterials 2009, 30, 1962]. When incorporated into micelles, a SPION has a longer half-life in circulation, improved biocompatibility, and shows better contrast. SPION polymeric micelles were used successfully as MRI probes and for drug delivery [N. Nasongkla, et al., Nano Letters 2006, 6, 2427; X. T. Shuai, et al., Journal of Controlled Release 2004, 98, 41; J. S. Guthi, et al., Molecular Pharmaceutics 2010, 7, 32; G. B. Hong, et al. Biomedical Microdevices 2008, 10, 693], but they have not been tested for gene delivery.